Horton

Re: Speed up Clog Access by increasing CLOG buffers

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-09-26T18:48:55Z
Lists: pgsql-hackers 
On 09/26/2016 07:16 PM, Tomas Vondra wrote:
>
> The averages (over the 10 runs, 5 minute each) look like this:
>
>  3.2.80                 1      8     16     32     64    128    192
> --------------------------------------------------------------------
>  granular-locking    1567  12146  26341  44188  43263  49590  15042
>  no-content-lock     1567  12180  25549  43787  43675  51800  16831
>  group-update        1550  12018  26121  44451  42734  51455  15504
>  master              1566  12057  25457  42299  42513  42562  10462
>
>  4.5.5                  1      8     16     32     64    128    192
> --------------------------------------------------------------------
>  granular-locking    3018  19031  27394  29222  32032  34249  36191
>  no-content-lock     2988  18871  27384  29260  32120  34456  36216
>  group-update        2960  18848  26870  29025  32078  34259  35900
>  master              2984  18917  26430  29065  32119  33924  35897
>
> That is:
>
> (1) The 3.2.80 performs a bit better than before, particularly for 128
> and 256 clients - I'm not sure if it's thanks to the reboots or so.
>
> (2) 4.5.5 performs measurably worse for >= 32 clients (by ~30%). That's
> a pretty significant regression, on a fairly common workload.
>

FWIW, now that I think about this, the regression is roughly in line 
with my findings presented in my recent blog post:

     http://blog.2ndquadrant.com/postgresql-vs-kernel-versions/

Those numbers were collected on a much smaller machine (2/4 cores only), 
which might be why the difference observed on 32-core machine is much 
more significant.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Use group updates when setting transaction status in clog.

  2. Improve 64bit atomics support.

  3. Add ProcArrayGroupUpdate wait event.

  4. Make the different Unix-y semaphore implementations ABI-compatible.

  5. Fix broken ALTER INDEX documentation

  6. Code and docs review for commit 3187d6de0e5a9e805b27c48437897e8c39071d45.

  7. Partition the freelist for shared dynahash tables.

  8. Correct StartupSUBTRANS for page wraparound

  9. Make idle backends exit if the postmaster dies.

  10. contrib/sslinfo: add ssl_extension_info SRF

  11. Reduce ProcArrayLock contention by removing backends in batches.

  12. Fix `make installcheck` for serializable transactions.

  13. Lockless StrategyGetBuffer clock sweep hot path.

  14. Reduce sinval synchronization overhead.